The present invention relates to a micromanipulator for moving objects, in particular for moving small objects over microscopic distances. The precision of the fine mechanical adjusting elements equipped with micrometer screws that are frequently utilized for these motions is often insufficient for motions in modern microtechnology. These adjusting elements are also not suited for application in high-vacuum or other closed systems, in which mechanical execution is a source of disturbance. Better suited for applications of this type are electromagnetically operated adjusting elements or adjustment elements based on the piezo-electric effect.
A micromanipulator with which piezo-electric motion elements are used for moving objects is described in DE-OS 36 10 540. Due to the attainable deformation of the motion elements with the piezo-electric effect, there are at least two limitations to these micromanipulators. First, the individual steps of the motion are limited to the nm range so that a great many steps have to be performed over large distances for the motion. Second, the individual moving elements must not be dimensioned too small as the maximum achievable span of the step is diminished with a decreasing size of the moving elements, thereby limiting miniaturization of the manipulator.
An object of the present invention is to provide a micromanipulator for moving objects permitting variable step spans in a range up to approximately 100 .mu.m while maintaining high precision of the motion and a high degree of miniaturization.
The aforesaid object has been achieved in accordance with the present invention by providing the mechanical elements of the micromanipulators as movable tongues composed of superimposed layers of different materials having varying thermal expansion coefficients.
The tongues are heated by energy input. As a tongue is composed of at least two layers having varying thermal expansion coefficients, the heat causes the tongue to bend. Objects can be moved by suited coordination of the motions of several tongues of a micromanipulator.
In order to obtain a linear motion of an object, the tongues can be arranged in pairs in such a manner that two tongues are lying opposite each other turned at 180.degree..
The basic body of the micromanipulator can be made of silicon; a material widely used in industrial micro-electronics is thus utilized as the basic material. In order to obtain as great as possible motion steps at low heat levels, the tongue is made of a combination of materials having thermal expansion coefficients varying as much as possible. The combination of a layer of silicon compound (e.g., silicon nitrate or silicon dioxide) and a metal layer accommodate microstructure fabrication processes.
The temperature is raised by heating elements. In principle, however, it could also be achieved with other methods, e.g., thermal radiation. It is advantageous to construct the heating elements as electric resistances and to dispose them between or onto the layers in order to ensure even heating.
In order to exclude the influence of the ambient temperature on the position of the tongues, an especially favorable arrangement can be obtained, in which sensor elements are disposed on the tongues in order to detect the momentary position and in order to regulate the position. They can be based on various physical effects. The use of piezoresistances is especially advantageous as the static piezoresistive effect is particularly pronounced with silicon and the position of the tongues can be determined directly by measuring the pull and pressure load. Another advantage is that piezoresistances can be easily fabricated with the aid of conventional microelectronic techniques. The heating and sensor signals are linked to each other in mutual control circuits, whereby the tongues can be brought to the predeterminable positions, by way of illustration, by regulating the heat input. In this way, the motions of the tongues can be coordinated and the span of the steps can be determined. The design and operation of the individual gripping elements correspond to the steerable, position changing elements described in the unpublished German application DE 38 09 587.1.
In order to obtain a high degree of miniaturization, the control circuits and the micromanipulator are integrated on the same semiconductor chip. In this way, micromanipulators can be fabricated, which are composed of a great number of identical tongues, thereby making complicated motions possible even over a distance of many step spans.
If the tongue pairs are arranged along a line, the objects can be moved in a one-dimensional direction. By arranging the pairs of tongues along several parallel lines, the weight to be transported can be increased.
The tongue parts can also be arranged along two groups of intersecting parallel lines. This embodiment of the present invention permits any desired motion in a plane. A rotary motion can be obtained by an arrangement of the tongues along concentric circular lines, with the axis of rotation being perpendicular to the plane in which the tongue pairs are arranged.
Furthermore, a tilting motion about small angles is also possible in that the loose ends of the tongues supporting the object carrier at various points can be moved different distances away from the basic body. By steering out all the tongues simultaneously, the object can also be moved to a limited extent in a perpendicular direction to the plane in which the tongues are arranged. This motion, which is restricted by the length of the tongues, is extremely advantageous if the object, by way of illustration, is to be aligned in the focus of a beam of light or of electrons. All the described embodiments of the present invention are fabricated with processes known in micromechanics and in micro-electronics and are compatible to standard IC processes. The individual components are structured with the aid of planar lithography processes. The voltage level customary in micro-electronics suffices for operating a micromanipulator.
The micromanipulator of the present invention in its several embodiments is distinguished by having a high degree of miniaturization, high precision, great reliability and low costs. It is especially suited for moving objects in closed systems in which mechanical operation must be avoided, by way of illustration, in ultra-high vacuum apparatuses (e.g., raster electron microscopy). The extreme degree of miniaturization permits utilization in microhandling systems and in any kind of moving of objects in microscopic examinations, in processing or analyzing objects in microtechnology or in microbiology.